Removal of Microcystin-LR from Drinking Water Using a System Involving Oxidation and Adsorption
2017
Lopes, WiltonS. | Buriti, JosuéS. | Cebalos, BeatrizS. O. | Sousa, JoséT. | Leite, ValderiD. | Vieira, FernandoF.
The aim of the present study was to evaluate the efficiency of removal of microcystin-LR from drinking water using a three-stage bench-scale treatment comprising Fenton oxidation/coagulation/flocculation/sedimentation, filtration through a sand column (15 cm bed), and adsorption onto a granular activated carbon (GAC) column with 15-cm (GAC1) or 20-cm bed (GAC2). Optimal first-stage conditions were determined to be FeSO₄∙7H₂O 0.054 mM, H₂O₂ 0.162 mM, coagulation pH 8.4, sedimentation time 15 min, and flow rate 2 L h⁻¹. Under these conditions, water turbidity was reduced from 5.8 to 3.0 uT, apparent color from 115 to 81 uH, and the concentration of microcystin-LR from 18.52 to 9.59 μg L⁻¹. Column GAC2 was more efficient than GAC1, as shown by the higher adsorption capacity (4.15 μg g⁻¹) and lower carbon usage rate (1.70 g L⁻¹). Microcystin breakthrough occurred after 2 h of operation with GAC1 column and after 6 h with GAC2 column, and the greater efficiency of the latter column was confirmed by the high qe (4.15 μg g⁻¹) and low CUR (1.70 g L⁻¹) values attained. The results demonstrate that adsorption on a GAC column plays an essential role in reducing the concentration of microcystin-LR to levels compatible with current legislation. By-products of the Fenton oxidation of microcystin-LR were analyzed by mass spectrometry, and the ADDA amino acid present in the analyte was identified from its characteristic fragment at m/z 135. It is concluded that the combination of Fenton oxidation and adsorption on a GAC column represents a viable option for purifying eutrophic water containing high concentrations of microcystin-LR.
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